Rates of decomposition of nifedipine in fluorescent and UV light were determined using stability specific HPLC and UV methods. The photodecomposition was zero order when the nifedipine concentrations were high enough to completely absorb the incident light and zero order rate was directly proportional to the intensity of light. At low concentrations of nifedipine, the reaction was first order. The rate of nifedipine photodecomposition was approximately three fold faster in organic solvents (methanol, ethanol, hexane) compared to that in water. The rate in 4% albumin and in human plasma were similar to the rates in organic solvent. Although several experiments were designed to understand why the rates in water was different (including studies in deuterated water, studying several related analogs), we have not yet found a satisfactory explanation.